U.S. patent application number 13/174420 was filed with the patent office on 2012-06-28 for cognitive radio cooperative spectrum sensing method and fusion center performing cognitive radio cooperative spectrum sensing.
This patent application is currently assigned to POSTECH ACADEMY - INDUSTRY FOUNDATION. Invention is credited to Jun Heo, Jae Young Lee, Chong Joon You.
Application Number | 20120163355 13/174420 |
Document ID | / |
Family ID | 46316731 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120163355 |
Kind Code |
A1 |
Heo; Jun ; et al. |
June 28, 2012 |
COGNITIVE RADIO COOPERATIVE SPECTRUM SENSING METHOD AND FUSION
CENTER PERFORMING COGNITIVE RADIO COOPERATIVE SPECTRUM SENSING
Abstract
Provided are a cognitive radio (CR) cooperative spectrum sensing
method and a fusion center (FC) performing CR cooperative spectrum
sensing. The CR cooperative spectrum sensing method includes
receiving, at an FC, local spectrum sensing information about a
predetermined frequency band from each of N secondary users (SUs)
in a predetermined zone, determining, at the FC, the optimum number
of SUs for determining whether the predetermined frequency band is
being used by a primary user (PU) on the basis of the received
local spectrum sensing information, and performing cooperative
spectrum sensing on the basis of local spectrum sensing information
received from the optimum number of SUs in the predetermined zone.
The method is implemented by the FC. Accordingly, the method and FC
find how many SUs are needed to determine that a frequency of a PU
is being used in a corresponding-channel situation, thereby
enabling efficient communication.
Inventors: |
Heo; Jun; (Seoul, KR)
; You; Chong Joon; (Seoul, KR) ; Lee; Jae
Young; (Seoul, KR) |
Assignee: |
POSTECH ACADEMY - INDUSTRY
FOUNDATION
Gyeongbuk
KR
|
Family ID: |
46316731 |
Appl. No.: |
13/174420 |
Filed: |
June 30, 2011 |
Current U.S.
Class: |
370/338 ;
455/507 |
Current CPC
Class: |
H04W 84/18 20130101;
H04W 16/14 20130101 |
Class at
Publication: |
370/338 ;
455/507 |
International
Class: |
H04W 24/00 20090101
H04W024/00; H04W 84/02 20090101 H04W084/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2010 |
KR |
10-2010-0136851 |
Claims
1. A cognitive radio (CR) cooperative spectrum sensing method,
comprising: receiving, at a fusion center (FC), local spectrum
sensing information about a predetermined frequency band from each
of N secondary users (SUs) in a predetermined zone; determining, at
the FC, an optimum number of SUs for determining whether the
predetermined frequency band is being used by a primary user (PU)
on the basis of the received local spectrum sensing information;
and performing cooperative spectrum sensing on the basis of local
spectrum sensing information received from the optimum number of
SUs in the predetermined zone.
2. The CR cooperative spectrum sensing method of claim 1, wherein
the local spectrum sensing information is a determination signal
indicating a determination of whether or not the predetermined
frequency band is being used by the PU made by the SUs.
3. The CR cooperative spectrum sensing method of claim 2, wherein
determining, at the FC, the optimum number of SUs includes:
providing a threshold of energy detection for generating the
determination signal, a signal-to-noise ratio (SNR) of an additive
white Gaussian noise (AWGN) channel, and a time-bandwidth product
that is a product of a measurement time for generating the
determination signal and a bandwidth of the predetermined frequency
band; calculating miss-detection probabilities, false alarm
probabilities, and predetermined frequency band use probabilities
of the SUs on the basis of the threshold, the SNR, the
time-bandwidth product, and the local spectrum sensing information;
and calculating the optimum number of SUs on the basis of the
miss-detection probabilities, the false alarm probabilities, and
the predetermined frequency band use probabilities.
4. The CR cooperative spectrum sensing method of claim 3, wherein
calculating the optimum number of SUs includes: calculating a
number {tilde over (K)} minimizing an overall detection error
probability using the equation, K ~ = ln ( P ( H 1 ) P m N P ( H 0
) ( 1 - P f ) N ) ln ( P f P m ( 1 - P f ) ( 1 - P m ) )
##EQU00006## where P(H.sub.1) is a probability that the PU will be
using the predetermined frequency band, P(H.sub.0) is a probability
that the PU will not be using the predetermined frequency band,
P.sub.m is a miss-detection probability of an SU (probability that
the SU cannot detect a signal transmitted from the PU), P.sub.f is
a false alarm probability of the SU, and N is the number of SUs in
the predetermined zone; and determining a natural number closest to
{tilde over (K)} as the optimum number of SUs.
5. The CR cooperative spectrum sensing method of claim 1, wherein
the predetermined zone is a wireless fidelity (Wi-Fi) zone, and the
FC is an access point (AP) for Wi-Fi.
6. A fusion center (FC) performing cognitive radio (CR) cooperative
spectrum sensing, comprising: a receiver configured to receive
local spectrum sensing information about a predetermined frequency
band from each of N secondary users (SUs) in a predetermined zone;
an SU number determiner connected with the receiver and configured
to determine an optimum number of SUs for determining whether the
predetermined frequency band is being used by a primary user (PU)
on the basis of the received local spectrum sensing information;
and a cooperative spectrum sensor connected with the receiver and
the SU number determiner, and configured to perform cooperative
spectrum sensing on the basis of local spectrum sensing information
received from the optimum number of SUs in the predetermined zone
determined by the SU number determiner.
7. The FC of claim 6, wherein the local spectrum sensing
information is a determination signal indicating a determination of
whether or not the predetermined frequency band is being used by
the PU made by the SUs.
8. The FC of claim 7, further comprising a storage configured to
store a threshold of energy detection for generating the
determination signal, a signal-to-noise ratio (SNR) of an additive
white Gaussian noise (AWGN) channel, and a time-bandwidth product
that is a product of a measurement time for generating the
determination signal and a bandwidth of the predetermined frequency
band, wherein the SU number determiner calculates miss-detection
probabilities, false alarm probabilities, and predetermined
frequency band use probabilities of the SUs on the basis of the
threshold, the SNR, the time-bandwidth product, and the local
spectrum sensing information, and calculates the optimum number of
SUs on the basis of the miss-detection probabilities, the false
alarm probabilities, and the predetermined frequency band use
probabilities.
9. The FC of claim 8, wherein the SU number determiner calculates a
number {tilde over (K)} minimizing an overall detection error
probability using the equation, K ~ = ln ( P ( H 1 ) P m N P ( H 0
) ( 1 - P f ) N ) ln ( P f P m ( 1 - P f ) ( 1 - P m ) )
##EQU00007## where P(H.sub.1) is a probability that the PU will be
using the predetermined frequency band, P(H.sub.0) is a probability
that the PU will not be using the predetermined frequency band,
P.sub.m is a miss-detection probability of an SU (probability that
the SU cannot detect a signal transmitted from the PU), P.sub.f is
a false alarm probability of the SU, and N is the number of SUs in
the predetermined zone, and determines a natural number closest to
{tilde over (K)} as the optimum number of SUs.
10. The FC of claim 6, wherein the predetermined zone is a wireless
fidelity (Wi-Fi) zone, and the FC is an access point (AP) for
Wi-Fi.
Description
CLAIM FOR PRIORITY
[0001] This application claims priority to Korean Patent
Application No. 10-2010-0136851 filed on Dec. 28, 2010 in the
Korean Intellectual Property Office (KIPO), the entire contents of
which are hereby incorporated by reference.
BACKGROUND OF INVENTION
[0002] 1. Technical Field
[0003] Example embodiments of the present invention relate to a
national research and development project having subject No.
ITAC1090103100090001000100100, project name "University IT Research
Center Promotion and Support Project," and subject title "Research
on Embedded Software Technology for Convergence Terminal."
[0004] Example embodiments of the present invention relate in
general to radio communication, and more specifically, to a
cognitive radio (CR) cooperative spectrum sensing method and a
fusion center (FC) performing CR cooperative spectrum sensing.
[0005] 2. Related Art
[0006] Currently, radio communication technology is being
researched and developed for a ubiquitous network in which any
information can be exchanged with anybody, anytime, anywhere.
Conventionally used for mobile communication and broadcasting,
radio waves are increasingly used in other areas of life, such as
traffic, medical treatment, science, and public order, rapidly
driving up demand for frequency resources. This increasing demand
for frequency resources is further accelerated by advances in radio
communication technology. To solve the frequency shortage problem
and maximize efficiency in frequency usage, CR technology for
detecting vacant frequencies that are not actually being used and
performing communication is attracting attention.
[0007] CR technology automatically enables desired communication by
automatically detecting unused frequencies according to place and
time while protecting authorized adjacent radio stations. The CR
technology detects a spectrum that is dispersed at various
intervals and has continuously varying occupation time, and enables
the spectrum to be reused by determining a frequency bandwidth,
output, modulation scheme, etc. appropriate for the environment,
thereby improving the efficiency with which limited frequency
resources are utilized. Since 2004, the Institute of Electrical and
Electronics Engineers (IEEE) has been pushing ahead with the
standardization of CR technology for a television frequency
band.
[0008] CR technology is based on spectrum sensing techniques which
allow a secondary user (SU) to sense the surrounding radio
environment and detect a vacant frequency band that a primary user
(PU) is not using. The spectrum sensing techniques include matched
filter, signal feature detection, energy detection, and so on.
Among the spectrum sensing techniques, energy detection can be
implemented even when a feature of a signal to be transmitted is
unknown, and is most appropriate in consideration of complexity and
sensing time. However, when one SU separately performs spectrum
sensing, the SU may not accurately detect a vacant frequency band
because of hidden nodes, shadow fading, multipath fading, etc. To
solve these problems, a cooperative spectrum sensing technique has
appeared, in which results separately sensed by SUs are shared in
an FC to determine whether or not a spectrum is occupied.
[0009] Cooperative spectrum sensing includes soft decision in which
results observed by several SUs are first transmitted to an FC
which then makes a final decision on the basis of the results, and
hard decision in which respective SUs first determine whether or
not a spectrum is used and then transmit the results to an FC which
makes a final decision. When respective soft decision results of CR
SUs are transmitted to an FC, frequency efficiency is degraded.
Thus, hard decision cooperative spectrum sensing is frequently
used.
[0010] In such hard decision cooperative spectrum sensing, whether
the corresponding frequency band is vacant or in use is determined
with reference to a threshold .lamda. of energy detection. In other
words, 1, indicating that the frequency band is in use, is
transmitted when energy is greater than .lamda., and 0, indicating
that the frequency band is not in use, is transmitted when energy
is smaller than .lamda.. Then, an FC makes a final decision using
the CR information (0 or 1) transmitted by an SU, according to a
fusion rule used in the FC.
REFERENCE
Patent Document
[0011] (Patent Reference 0001) US 2010/0248760 A1. Publication
date: Sep. 30, 2010, Title: System and method for cooperative
spectrum sensing in cognitive radio systems
Non-Patent Document
[0011] [0012] (Non-patent Reference 0001) [Document 1] J. Mitola
and G. Q. Maguire, "Cognitive radio: Making software radios more
personal," IEEE Pers. Commun., vol. 6, pp. 13-18, August 1999. This
reference proposed Cognitive Radio for the first time. [0013]
(Non-patent Reference 0002) [Document 2] A. Ghasemi, E. S. Sousa,
"Collaborative spectrum sensing for opportunistic access in fading
environments," In Proc., IEEE. Inter. Symp. Dyspan 2005, pp.
131-136, November 2005. This reference proposed Cooperative
Spectrum Sensing for the first time. [0014] (Non-patent Reference
0003) [Document 3] F. F. Digham, M. S. Alouini, et al., "On the
energy detection of unknown signals over fading channels," IEEE
Transactions on Communications, vol. 55, No. 1, pp. 21-24, January
2007. This reference discloses miss-detection probability and false
alarm probability of an energy detection technique as numerical
expressions.
SUMMARY OF INVENTION
[0015] Accordingly, example embodiments of the present invention
are provided to substantially obviate one or more problems due to
limitations and disadvantages of the related art.
[0016] Example embodiments of the present invention provide a
cognitive radio (CR) cooperative spectrum sensing method capable of
determining the optimum number of secondary users (SUs) for
determining that a primary user (PU) is using a predetermined
frequency band.
[0017] Example embodiments of the present invention also provide a
fusion center (FC) for implementing the method.
[0018] In some example embodiments, a CR cooperative spectrum
sensing method includes: receiving, at an FC, local spectrum
sensing information about a predetermined frequency band from each
of N number of SUs in a predetermined zone; determining, at the FC,
the optimum number of SUs for determining whether the predetermined
frequency band is being used by a PU on the basis of the received
local spectrum sensing information; and performing cooperative
spectrum sensing on the basis of local spectrum sensing information
received from the optimum number of SUs in the predetermined
zone.
[0019] The local spectrum sensing information may be a
determination signal indicating a determination of whether or not
the predetermined frequency band is being used by the PU made by
the SUs.
[0020] Determining, at the FC, the optimum number of SUs may
include: providing a threshold of energy detection for generating
the determination signal, a signal-to-noise ratio (SNR) of an
additive white Gaussian noise (AWGN) channel, and a time-bandwidth
product that is a product of a measurement time for generating the
determination signal and a bandwidth of the predetermined frequency
band; calculating miss-detection probabilities, false alarm
probabilities, and predetermined frequency band use probabilities
of the SUs on the basis of the threshold, the SNR, the
time-bandwidth product, and the local spectrum sensing information;
and calculating the optimum number of SUs on the basis of the
miss-detection probabilities, the false alarm probabilities, and
the predetermined frequency band use probabilities.
[0021] Calculating the optimum number of SUs may include:
calculating a number {tilde over (K)} minimizing an overall
detection error probability using the following equation:
K ~ = ln ( P ( H 1 ) P m N P ( H 0 ) ( 1 - P f ) N ) ln ( P f P m (
1 - P f ) ( 1 - P m ) ) ##EQU00001##
[0022] Here, P(H1) is a probability that the PU will be using the
predetermined frequency band, P(H0), is a probability that the PU
will not be using the predetermined frequency band, Pm is a
miss-detection probability of an SU (a probability that the SU
cannot detect a signal transmitted from the PU), Pf is a false
alarm probability of the SU, and N is the number of SUs in the
predetermined zone; and determining a natural number closest to
{tilde over (K)} as the optimum number of SUs.
[0023] The predetermined zone may be a wireless fidelity (Wi-Fi)
zone, and the FC may be an access point (AP) for Wi-Fi.
[0024] In other example embodiments, an FC performing CR
cooperative spectrum sensing includes: a receiver configured to
receive local spectrum sensing information about a predetermined
frequency band from each of N number of SUs in a predetermined
zone; an SU number determiner connected with the receiver and
configured to determine the optimum number of SUs for determining
whether the predetermined frequency band is being used by a PU on
the basis of the received local spectrum sensing information; and a
cooperative spectrum sensor connected with the receiver and the SU
number determiner, and configured to perform cooperative spectrum
sensing on the basis of local spectrum sensing information received
from the optimum number of SUs in the predetermined zone determined
by the SU number determiner.
[0025] The local spectrum sensing information may be a
determination signal indicating a determination of whether or not
the predetermined frequency band is being used by the PU made by
the SUs.
[0026] The FC may further include a storage configured to store a
threshold, an SNR, and a time-bandwidth product wherein the
threshold may be a threshold of energy detection for generating the
determination signal, wherein the SNR may be an SNR of an AWGN
channel, and wherein the time-bandwidth product may be a product of
a measurement time for generating the determination signal and the
bandwidth of the predetermined frequency band, and the SU number
determiner may calculate miss-detection probabilities, false alarm
probabilities, and predetermined frequency band use probabilities
of the SUs on the basis of the threshold, the SNR, the
time-bandwidth product, and the local spectrum sensing information,
and calculate the optimum number of SUs on the basis of the
miss-detection probabilities, the false alarm probabilities, and
the predetermined frequency band use probabilities.
[0027] The SU number determiner may calculate a number {tilde over
(K)} minimizing an overall detection error probability using the
following equation:
K ~ = ln ( P ( H 1 ) P m N P ( H 0 ) ( 1 - P f ) N ) ln ( P f P m (
1 - P f ) ( 1 - P m ) ) , ##EQU00002##
and determine a natural number closest to {tilde over (K)} as the
optimum number of SUs. Here, P(H1) is a probability that the PU
will be using the predetermined frequency band, P(H0) is a
probability that the PU will not be using the predetermined
frequency band, Pm is a miss-detection probability of an SU
(probability that the SU cannot detect a signal transmitted from
the PU), Pf is a false alarm probability of the SU, and N is the
number of SUs in the predetermined zone.
BRIEF DESCRIPTION OF DRAWINGS
[0028] Example embodiments of the present invention will become
more apparent by describing in detail example embodiments of the
present invention with reference to the accompanying drawings, in
which:
[0029] FIG. 1 schematically illustrates an overall wireless
communication network including a fusion center (FC) according to
an example embodiment of the present invention when a television
frequency band is used by secondary users (SUs) in a wireless
fidelity (Wi-Fi) zone;
[0030] FIG. 2 is a block diagram of an FC according to an example
embodiment of the present invention;
[0031] FIG. 3 is a flowchart illustrating operation of the FC of
FIG. 2;
[0032] FIG. 4 is a graph of detection error probability,
miss-detection probability, and false alarm probability versus SU
threshold number; and
[0033] FIG. 5 is a graph of optimum SU threshold number versus
miss-detection probability.
DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE PRESENT INVENTION
[0034] Example embodiments of the present invention are disclosed
herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of
describing example embodiments of the present invention. Example
embodiments of the present invention may be embodied in many
alternate forms and should not be construed as limited to example
embodiments of the present invention set forth herein.
[0035] Accordingly, while the invention is susceptible to various
modifications and alterations in form, specific embodiments thereof
are shown by way of example in the drawings and will herein be
described in detail. It should be understood, however, that there
is no intent to limit the invention to the particular forms
disclosed. On the contrary, the invention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention. Like numbers refer to like
elements throughout the description and the figures.
[0036] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of the present invention. As used herein, the term "and/or"
includes any and all combinations of one or more of the associated
listed items.
[0037] It will be understood that when an element is referred to as
being "connected" or "coupled" to another element, it can be
directly connected or coupled to the other element or intervening
elements may be present. In contrast, when an element is referred
to as being "directly connected" or "directly coupled" to another
element, there are no intervening elements present. Other words
used to describe a spatial or sequential relationship between
elements should be interpreted in a like fashion (i.e., "between"
versus "directly between," "adjacent" versus "directly adjacent,"
etc.).
[0038] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a," "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises," "comprising," "includes" and/or
"including," when used herein, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0039] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0040] It should also be noted that in some alternative
implementations, the functions/acts noted in the blocks may occur
out of the order noted in the flowcharts. For example, two blocks
shown in succession may in fact be executed substantially
concurrently or the blocks may sometimes be executed in the reverse
order, depending upon the functionality/acts involved.
[0041] Hereinafter, example embodiments of the present invention
will be described with reference to appended drawings.
[0042] When K or more secondary users (SUs) among N number of SUs
send information "1", a fusion center (FC) generally determines
that a frequency band is in use as a final decision. Otherwise, the
FC determines that the frequency band is not in use.
[0043] Thus, it is necessary to find how many SUs need to detect
that a primary user (PU) is using a predetermined frequency band
using a cooperative spectrum sensing technique, in which several
SUs sense surrounding radio environments to detect a vacant
frequency band, in order to optimize performance by making a final
decision that the PU is using the frequency band.
[0044] An Institute of Electrical and Electronics Engineers (IEEE)
802.22 wireless regional area network includes three main
components: a PU, an SU, and an FC., The PU is a digital/analog
television channel, the SU is customer-premises equipment (CPE),
for example, a smartphone, laptop computer, netbook, and personal
digital assistant (PDA), in a wireless fidelity (Wi-Fi) zone, and
the FC is an access point (AP).
[0045] FIG. 1 illustrates an overall wireless communication network
including an FC according to an example embodiment of the present
invention. The overall wireless communication network shown in FIG.
1 includes a PU 11 and a Wi-Fi zone 13. The PU 11 may use a
television signal having a frequency band centered at, for example,
2.4 GHz. N number of SUs, that is, SU 1 to SU N, are included in
the Wi-Fi zone 13.
[0046] The SUs 1 to N determine whether the frequency band used by
the PU 11 is vacant or in use. The determination is made with
reference to a threshold .lamda. of energy detection. In other
words, "1," indicating that the frequency band is in use, is
generated as local spectrum sensing information when detected
energy is greater than .lamda., and "0," indicating that the
frequency band is not in use, is generated as local spectrum
sensing information when detected energy is smaller than .lamda..
Respective SUs transmit the local spectrum sensing information to
an FC 15.
[0047] The FC 15 makes a final decision whether the PU 11 is using
the frequency band using the local spectrum sensing information
transmitted by the respective SUs according to fusion rule used in
the FC 15. To make such a final decision, the FC 15 may receive
local spectrum sensing information from all the SUs 1 to N included
in the Wi-Fi zone 13. In this spectrum sensing technique, two types
of errors occur. One is a miss-detection error and the other is a
false alarm error. To minimize detection errors consisting of the
two types of error by making a final decision that the PR is using
the predetermined frequency band, the FC 15 determines the optimum
number of SUs required to detect that the PR is using the
predetermined frequency band.
[0048] Determination of the optimum number of SUs made by the FC 15
will be described with reference to FIGS. 2 and 3.
[0049] FIG. 2 is a block diagram showing the internal constitution
of the FC 15. In FIG. 2, the FC 15 has a transmitter 21 and a
receiver 22 connected with an antenna, a processor 24 connected
with the transmitter 21 and the receiver 22, and a memory 26
connected with the processor 24. The receiver 22 may receive local
spectrum sensing information from the SUs 1 to N in the Wi-Fi zone
13 shown in FIG. 1. The processor 24 determines the optimum number
of SUs using the received local spectrum sensing information and
data stored in the memory 26.
[0050] FIG. 3 is a flowchart illustrating operation of the FC 15
shown in FIG. 2. Operation of the FC 15 of FIG. 2 will be described
with reference to the flowchart of FIG. 3.
[0051] In the FC 15, the receiver 22 receives local spectrum
sensing information through the antenna (step 310). The local
spectrum sensing information may have a value of 1 or 0, that is a
determination signal resulting from a determination of whether or
not a PU is using a predetermined frequency band, made by an SU.
The receiver 22 provides the received local spectrum sensing
information to the processor 24.
[0052] The processor 24 determines the optimum number of SUs for
determining whether the PU is using the predetermined frequency
band on the basis of the received local spectrum sensing
information (step 330). The memory 26 stores data that is used for
the processor 24 to determine the optimum number of SUs.
[0053] To determine the optimum number of SUs, the processor 24
provides a threshold, a signal-to-noise ratio (SNR), and a
time-bandwidth product. In this step, the threshold is a threshold
.lamda. of energy detection for generating the determination
signal, the SNR is an SNR of an additive white Gaussian noise
(AWGN) channel, and the time-bandwidth product is a product of a
measurement time for generating the determination signal and the
bandwidth of the predetermined frequency band. Then, the processor
24 calculates miss-detection probabilities, false alarm
probabilities, and predetermined frequency band use probabilities
of SUs on the basis of the threshold .lamda., the SNR, the
time-bandwidth product, and the local spectrum sensing
information.
[0054] When the FC 15 calculates a final miss-detection probability
and a final false alarm probability using cooperative spectrum
sensing, an OR rule or AND rule may be used. The OR rule is a
fusion method in which the FC 15 determines that a PU signal exists
when at least one SU determines that the PU signal exists, and the
AND rule is a fusion method in which the FC 15 determines that a PU
signal exists only when all SUs determine that the PU signal
exists.
[0055] These two methods are extreme fusion methods and are not
efficient. Thus, example embodiments of the present invention use a
K-out-of-N rule, in which a final decision that a PU signal exists
is made when K or more SUs among a total of N SUs determine that
the PU signal exists. The K-out-of-N rule includes the OR rule when
K is 1, and the AND rule when K is N.
[0056] In cooperative spectrum sensing of several SUs according to
the K-out-of-N rule, an overall miss-detection probability and
false alarm probability may be expressed by Equation 1 below as a
combination of miss-detection probabilities and false alarm
probabilities respectively corresponding to the SUs. FIG. 4 is a
graph of Equation 1.
K - out - of - N - Rule { P m , t = 1 - j = K N ( N j ) ( 1 - P m )
j P m N - j P f , t = j K N ( N j ) P f j ( 1 - P f ) N - j [
Equation 1 ] ##EQU00003##
[0057] Here, Pm,t is a probability that a final decision made by an
FC will be a miss-detection error, and Pf,t is a probability that a
final decision of the FC will be a false alarm error.
[0058] Subsequently, the processor 24 calculates the optimum number
of SUs on the basis of the miss-detection probabilities, the false
alarm probabilities, and the predetermined frequency band use
probabilities.
[0059] To calculate the optimum number of SUs, the processor 24
calculates a number {tilde over (K)} minimizing an overall
detection error probability using Equation 2 below.
K ~ = ln ( P ( H 1 ) P m N P ( H 0 ) ( 1 - P f ) N ) ln ( P f P m (
1 - P f ) ( 1 - P m ) ) [ Equation 2 ] ##EQU00004##
[0060] Here, P(H1) is a probability that the PU will be using the
predetermined frequency band, P(H0) is a probability that the PU
will not be using the predetermined frequency band, Pm is a
miss-detection probability of an SU (probability that the SU cannot
detect a signal transmitted from the PU), Pf is a false alarm
probability of the SU, N is the number of SUs in the predetermined
zone. Then, the processor 24 determines a natural number closest to
{tilde over (K)} as the optimum number of SUs.
[0061] In cooperative spectrum sensing, detection errors need to be
minimized, and the minimum of K capable of minimizing detection
errors needs to be found. A final detection error probability Pe,t
may be expressed by Equation 3 below.
P.sub.e,f=P(H.sub.1)P.sub.m,t+P(H.sub.0)P.sub.f,t [Equation 3]
[0062] Inserting Equation 1 into Equation 3 yields Equation 4
below.
P e , t = P ( H 1 ) { 1 - j = K N ( N j ) ( 1 - P m ) j P m N - j }
+ P ( H 0 ) { j = K N ( N j ) P f j ( 1 - P f ) N - j } [ Equation
4 ] ##EQU00005##
[0063] When the optimum value of K minimizing the final detection
error probability Pe,t is {tilde over (K)}, the minimum is obtained
from Equation 5 below.
P.sub.e,t({tilde over (K)}-1)-P.sub.e,t({tilde over (K)}).apprxeq.0
[Equation 5]
[0064] By inserting Equation 3 into Equation 4 and simplifying
Equation 4, Equation 2 above is obtained.
[0065] Finally, the processor 24 performs cooperative spectrum
sensing on the basis of local spectrum sensing information received
from the optimum number of SUs in the Wi-Fi zone 13 (step 350).
[0066] Table 1 below shows the optimum number of SUs with respect
to specific Pm and Pf and all SUs in a predetermined frequency
band. Table 1 shows that a threshold of the optimum number of SUs
is 8 when Pm is 0.2, Pf is 0.2, and N is 15.
TABLE-US-00001 TABLE 1 P.sub.m = 0.2 P.sub.m = 0.1 P.sub.m = 0.05 N
P.sub.f = 0.2 P.sub.f = 0.3 P.sub.f = 0.35 15 8 10 11 19 10 13 14
23 12 15 17 25 13 16 18
[0067] Example embodiments of the present invention allow use of a
vacant TV frequency for Wi-Fi data transmission according to IEEE
802.22, etc., thereby improving Wi-Fi capacity. However, in order
to make a final decision and ensure reliability of a process of
sensing a vacant frequency, it is necessary to know how many SUs
need to detect that a PU is using a current frequency. Thus,
example embodiments of the present invention find how many (K
.quadrature..quadrature.) SUs are needed to determine that a
frequency of a PU is being used in a corresponding-channel
situation, thereby enabling efficient communication.
[0068] Example embodiments of the present invention can be used for
cognitive radio (CR) technology enabling SUs in a predetermined
zone to perform radio communication using a predetermined frequency
band that is not being used by a PU. Example embodiments of the
present invention can use a vacant frequency band of a television
frequency spectrum for Wi-Fi data transmission according to IEEE
802.22.
[0069] While the example embodiments of the present invention and
their advantages have been described in detail, it should be
understood that various changes, substitutions and alterations may
be made herein without departing from the scope of the
invention.
* * * * *